Current lead-in seal for electric vacuum tubes and the like



W. T. GIBSON CURRENT LEAD-IN SEAL FOR ELECTRIC 2 Sheets-Sheet 1 March 29, 1949.

VACUUM TUBES AND THE LIKE Filed March 26, 1945 Inventor March 29, 1949. w. T. GIBSON CURRENT LEAD-IN SEAL FOR ELECTRIC VACUUM TUBES AND THE LIKE 2 Sheets-Sheet 2 Filed March 26, 1945 F/GB.

In venlor Wmunm Tum Q-msou Atto ey Patented Mar. 29, 1949 CURRENT LEAD-IN SEAL FOR ELECTRIC VACUUM TUBES AND THE LIKE William Thomas Gibson, London, signor, by mesne assignments, Standard Electric Corporation,

England, asto International New York, N. Y.,

a corporation of Delaware Application March 26, 1945, Serial No. 584,801 In Great Britain March 3, 1944 The present invention relates to thermionic valves and other like electric vacuum or gasfilled tubes, and is particularly concerned with improving the arrangements for bringing the filament lead conductors outside the envelope in high power valves.

In valves of this kind it has previously been the practice to provide two co-axial copper tubes one inside the other to convey the heating current to and from the filament. The outer tube is sealed through the envelope, and the inner tube is sealed to the outer tube by means of a re-entrant annular glass bulb at some point outside the envelope. An arrangement of this kind may be seen, for example, in British Patent Specification No. 469,584. As there is usually some considerable length of copper tube between the external seal and the filament supports, trouble is likely to be experienced when the valve heats up from differences in expansion between the two tubes. The principal object of the present invention is to eliminate the effect of the difference of expansion and to accomplish this without the use of a flexible section in one of the tubes, and by means of a simple assembly.

The invention accordingly provides an electric vacuum or gas-filled valve comprising an envelope and two coaxial metal tubes arranged one inside the other, the outer tube being sealed through the said envelope, and the two tubes being fixed together at their ends inside the said envelope by an insulating seal hermetically closing the annular space between the two tubes, and the inner tube being closed at its inside end.

The invention will be described with reference to the-accompanying drawings in which Figures 1, 2, and 3 each shows a sectional view of the part of the envelope of a thermionic valve through which the lead-out conductors are sealed, each of said figures illustrating a different embodiment of the invention.

It will be convenient to describe Figs. 1 and 2 together, and the particulars given apply to both except where one of them is specially referred to. Many of the elements in these two figures are similar and are given the same designations.

As shown in Fig. 1 or 2, a valve according to the invention comprises an envelope i (see Fig. l) or a reentrant envelope to (see Fig. 2) of glass or the like, of which only the lower part is shown. This envelope encloses the usual valve electrodes, none of which is shown. The valve is of the filamentary type cathode (not shown) which may be arranged in one or more loops as shown in the above-mentioned patent specification, for

Claims. (Cl. 49-925) example. The lead-out conductors for the filament comprise two co-axial metal tubes 2 and 3, preferably of copper, arranged one inside the other. The outer tube 2 is sealed through the envelope by means of a flared metal cone 4 brazed or otherwise secured thereto at 5, and sealed to the envelope l or to at the lower end 6 or to by a Housekeeper seal, for example. In Fig. 1, the cone 4 is turned upwards, but in Fig. 2 it is turned downwards in order to accommodate the rc-entrant envelope la.

The outer tube 2 is flared out at its upper end, and the inner tube 3 is provided with a metal cone 1 brazed thereto. The two tubes are sealed together inside the envelope l by means of a glass ring 8 in Fig. 1 or as shown in Fig. 2, by a small ire-entrant annular channel-shaped glass bulb portion 9 sealed by Housekeeper seals to the two tubes. The inner tube 3 is hermetically closed at its upper end by a solid metal plug in secured thereto. This plug carries at its upper end a platform H to which one end of the filament (or of each of the loops thereof) may be secured in any convenient way. A metal cylinder i2, as shown in Fig. 1, is secured at [4 inside the envelope to the upper end of the tube 2 to which cylinder the other end of the filament or the other ends of its loops may be secured. By the alternative arrangement shown in Fig. 2, a metal rod such as i3 is secured at 5 to the tube 2 to serve for the filament connection. The cylinder [2 or the rod 53 may be of any suitable length.

It is to be noted that since the two metal tubes are joined together at their upper ends, there will be no appreciable relative movements of the platform H and cylinder l2 (or rod I3) caused by differences in expansion of the tubes when the valve becomes hot. Such movements may occur at the lower ends of the tubes where they do not matter, or can easily be dealt with. Another point is that the space between the two tubes is now in effect outside the envelope instead of inside as in the previous arrangement already referred to, and besides greatly simplifying the construction this also enables the tubes to be very easily cooled by means of water or air. For this purpose a hole It (or a series of holes) is provided through the wall of the inner tube 3 at the upper end. Air or water or other cooling fluid may thus be supplied through the inner tube and exhausted from the space between the tubes.

The tubes 2 and 3 can clearly be made of any suitable length outside the envelope; for example, they can be out quite short.

Fig. 3 shows another embodiment of the invention, which though in principle the same as those shown in Figs. 1 and 2 diifers therefrom in one or two particulars of practical importance. Those elements in Fig. 3 which are substantially similar to corresponding elements in Figs. 1 and 2 are given the same designations.

The two co-axial copper tubes 2 and 3 which serve as the filament leads are arranged as in Fig. 2 for a re-entrant envelope l which is sealed to a cone 4 brazed at E5 to the outer tube 2. The upper end of the inner tube 3 is closed by a copper disc I 7 brazed thereon, and a down turned copper cone i6 is brazed on to the outside of the tube 3. The upper end of the outer tube terminates in a cone Ill.

The two cones l8 and iii are sealed by a Housekeeper seal to opposite ends of a rbarrel-shaped ring of glass 29 which corresponds to the details 8 and 9 shown in Figs. 1 and 2 respectively. This arrangement enables the seals to be rather more easily made than the arrangement of Fig. 1 or 2, and the cone it, which corresponds to the cone 1 of Figs. 1 and 2 is turned downwards instead of upwards for this purpose.

A copper ring 2i is brazed on to the outside of the outer tube 2 and carries one or more leads or anchors 22 for the filament (not shown). Anchors 23 for the other ends of the filament are mounted in any convenient way in the disc ll.

Ihe two tubes 2 and 3 are spaced apart at the lower end by an annular insulator 24 which also provides some mechanical support. Two clamps (not shown) may be secured respectively to the two tubes 2 and 3 for making the connections to the external leads for the filament heating current.

The inner tube 3 has a large number of perforations 15. Air or other cooling fluid may be introduced into the tube 3 at 2i and escapes through the holes ill for the purpose of cooling the glass ring 26 and seals to the cones it and l 9, and may be exhausted from the space between the tubes through holes provided in the insulator 24.

The glass ring 28 may be very short since the voltage between the metal parts at its ends is only the filament voltage, which is quite low.

The filament supports 2! and 22 should be of relatively large cross-section so that they will be at substantially the same temperature as the tubes 2 and 3. Expansion or contraction of the short length between the disc ll" and the ring 2| are found to be negligible in practice, and it is easy to arrange so that the highest temperature reached in this area is from 100 C. to 150 C.

An alternative cooling arrangement is to provide a cylindrical baifie 2% in the space between the two tubes, the baflle being attached to the outer tube at the lower end of the bafiie, and extending to a position between the holes l5 and the glass ring re. A ring of exhaust holes is provided in the wall of the outer tube 2 at 29 just outside the envelope I, and air is blown into the space between the two tubes. Part of the air is exhausted through the holes at 29, and the rest through the holes l6, and out at El. This arrangement is a little more complicated than the simpler arrangement first descdbed, which is, however, found to be quite satisfactory in many cases.

Although the present invention is of particular interest in connection with high power valves which generally employ directly heated cathodes, it is evident that the tubes 2 and 3 in any of the embodiments could be used for the lead out conductors for the heater of an indirectly heated cathode.

The arrangement of the invention has the following advantages:

1. It has a rotational symmetry throughout, so that all machining and glass working can be easily done on a lathe.

2. The adverse effects of unequal expansion are avoided.

3. It provides a very simple means for leading very heavy currents into a valve.

4. It enables cooling to be easily applied to the filament lead out conductors.

5. The length can be quite short, since the tubes are joined inside the envelope.

What is claimed is:

1. A current lead-in seal for use in a hermetically sealed device having an envelope wherein the lead-in conductors undergo wide changes in temperature, said seal comprising a pair of con centric metallic tubes having one end thereof normally disposed inside of said sealed device, means for hermetically plugging the inner tube at said one end, an annular ring of insulating material sealed to said inner and outer tubes adjacent the one end thereof and sealing the space between said tubes, and an annular ring of metal sealed to said outer tube, a portion of said annular ring of metal at a region removed from said outer tube being adapted for scaling to said envelope.

2. The structure of claim 1 wherein means are provided between said tubes for supporting said tubes relative to each other at a portion remote from said one end to provide a rigid structure.

3. A current lead-in seal for use in a hermetically sealed device having an envelope wherein the lead-in conductors undergo wide changes in temperature, said seal comprising a pair of con centric metallic tubes having one end thereof normally disposed inside of said sealed device, insulating material fused to said tubes at said one end and forming a rigid sealing connection therebetween, means for hermetically plugging the inner tube at said one end, and means hermetically sealed to the outer tube at a zone near said one end and being adapted for sealing to said envelope.

4. The structure of claim 3 wherein the means for sealing to the envelope comprises a metal cone having the small end sealed to said outer tube and the flared end adapted for sealing to said envelope.

5. The structure of claim 3 wherein said inner tube has passages through the walls thereof giving fluid access to the annular region between said two concentric tubes whereby cooling fluid may be circulated.

6. A current lead-in seal for use in a hermetically sealed device having an envelope wherein the lead-in conductors undergo wide changes in emperature, said seal comprising a pair of concentric metallic tubes having one end thereof normally disposed inside of said sealed device, insulating material bridging the annular space between said tube ends at said one end and forming a rigid hermetic sealing connection therebetween, a metallic member hermetically plugging said inner tube at said one end and providing a platform from which electrodes may be supported, and an annular metal member sealed to said outer tube along a narrow circular zone and sealed to said envelope material along a narrow circular zone.

7. The structure of claim 6 wherein said concentric tubes are flared at said one end with said metallic member being disposed in the cylindrical part of said inner tube.

8. The structure of claim 6 wherein said inner tube has apertures therethrough giving access to the annular space between said tubes whereby cooling fluid may be circulated between said two concentric tubes.

9. A current lead-in seal for use in a hermetically sealed device having a glass envelope wherein the lead-in conductors undergo wide changes in temperature, said seal comprising a pair of concentric metallic tubes having one end thereof normally disposed inside of said glass envelope, glass fused to said tubes at said one end and forming an annular seal between said tubes, a metal plug hermetically sealing the inner tube at said one end, and a metal ring surrounding said outer tube and having one portion sealed thereto and having another portion sealed to said glass envelope, said ring providing a hermetic circular seal between said glass envelope and outer tube.

10. A current lead-in seal according to claim 3 wherein a metallic cone is sealed to said inner tube, said metallic cone extending towards said outer tube, said outer tube being terminated by a cone extending towards said metallic cone, and said sealing means comprises a barrel-shaped insulating portion sealed between the opposite ends of said cones.

WILLIAM THOMAS GIBSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,900,109 Hendry Mar. 7, 1933 1,912,097 Rinia May 30, 1933 FOREIGN PATENTS Number Country Date 530,417 Germany July 29, 1931 Certificate sf errection Patent No. 2,465,369 March 29, 1949 WILLIAM THOMAS GKBSON It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 17, strike out the words of seventeen years same line, after grant insert until Il larch 3, 1 964; in the heading to the printe i specification, line 10, before 10 Claims insert the ioiiowing: Sect ice 1, Public Law 690, August 8,

1946, Patent expires March 3, 1 964.; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day oi June, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gommissioner of Patents.

1' Gertificate of Qerrection Patent No. 2,465,369 March 29, 1949 WILLIAM THOMAS GIBSON It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 17, strike out the words of seventeen years same line, after grant insert until March 3, 1964; in the heading to the printed specification, line 10, before 10 Claims insert the following: Section 1, Public Law 690, August 8, 1946, Patent expires March 8, 1964.; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 20th day of June, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommtssioner of Patents. 

